diff --git a/scrapy/contrib/resolver.py b/scrapy/contrib/resolver.py
new file mode 100644
index 000000000..b688a56c3
--- /dev/null
+++ b/scrapy/contrib/resolver.py
@@ -0,0 +1,45 @@
+from collections import defaultdict
+
+from twisted.internet import reactor, defer
+from twisted.internet.base import ThreadedResolver
+
+from scrapy.xlib.pydispatch import dispatcher
+from scrapy.utils.httpobj import urlparse_cached
+from scrapy.core import signals
+
+
+class CachingResolver(object):
+    """Scrapy extension to use a caching resolver, instead of default one"""
+
+    def __init__(self):
+        self.spider_hostnames = defaultdict(set)
+        self.resolver = _CachingThreadedResolver(reactor)
+        reactor.installResolver(self.resolver)
+        dispatcher.connect(self.request_received, signals.request_received)
+        dispatcher.connect(self.domain_closed, signal=signals.domain_closed)
+
+    def request_received(self, request, spider):
+        url_hostname = urlparse_cached(request).hostname
+        self.spider_hostnames[spider.domain_name].add(url_hostname)
+
+    def domain_closed(self, spider):
+        for hostname in self.spider_hostnames:
+            self.resolver._cache.pop(hostname, None)
+
+
+class _CachingThreadedResolver(ThreadedResolver):
+
+    def __init__(self, *args, **kwargs):
+        ThreadedResolver.__init__(self, *args, **kwargs)
+        self._cache = {}
+
+    def getHostByName(self, name, timeout = (1, 3, 11, 45)):
+        if name in self._cache:
+            return defer.succeed(self._cache[name])
+        dfd = ThreadedResolver.getHostByName(self, name, timeout)
+        dfd.addCallback(self._cache_result, name)
+        return dfd
+
+    def _cache_result(self, result, name):
+        self._cache[name] = result
+        return result
diff --git a/scrapy/core/downloader/manager.py b/scrapy/core/downloader/manager.py
index ef513418c..685a206e3 100644
--- a/scrapy/core/downloader/manager.py
+++ b/scrapy/core/downloader/manager.py
@@ -13,7 +13,6 @@ from scrapy.utils.defer import mustbe_deferred
 from scrapy import log
 from .middleware import DownloaderMiddlewareManager
 from .handlers import download_any
-from .resolver import CachingThreadedResolver
 
 
 class SiteInfo(object):
@@ -55,8 +54,6 @@ class Downloader(object):
         self.sites = {}
         self.middleware = DownloaderMiddlewareManager()
         self.concurrent_domains = settings.getint('CONCURRENT_DOMAINS')
-        cached_resolver = CachingThreadedResolver(reactor)
-        reactor.installResolver(cached_resolver)
 
     def fetch(self, request, spider):
         """ Main method to use to request a download
diff --git a/scrapy/core/downloader/resolver.py b/scrapy/core/downloader/resolver.py
deleted file mode 100644
index 596f5b3e4..000000000
--- a/scrapy/core/downloader/resolver.py
+++ /dev/null
@@ -1,29 +0,0 @@
-"""DNS resolver with cache to use with Twisted reactors"""
-
-from twisted.internet import defer
-from twisted.internet.base import ThreadedResolver
-
-from scrapy.core import signals
-from scrapy.xlib.pydispatch import dispatcher
-
-class CachingThreadedResolver(ThreadedResolver):
-
-    def __init__(self, reactor):
-        ThreadedResolver.__init__(self, reactor)
-        self._cache = {}
-        dispatcher.connect(self.domain_closed, signal=signals.domain_closed)
-
-    def getHostByName(self, name, timeout = (1, 3, 11, 45)):
-        if name in self._cache:
-            return defer.succeed(self._cache[name])
-        dfd = ThreadedResolver.getHostByName(self, name, timeout)
-        dfd.addCallback(self._cache_result, name)
-        return dfd
-
-    def _cache_result(self, result, name):
-        self._cache[name] = result
-        return result
-
-    def domain_closed(self, spider):
-        for domain in [spider.domain_name] + spider.extra_domain_names:
-            self._cache.pop(domain, None)