diff --git a/cache/stores/memcached/lib.php b/cache/stores/memcached/lib.php
index 56df93771b9..ba7a6d55295 100644
--- a/cache/stores/memcached/lib.php
+++ b/cache/stores/memcached/lib.php
@@ -229,8 +229,56 @@ class cachestore_memcached extends cache_store implements cache_is_configurable
         $version = phpversion('memcached');
         $this->candeletemulti = ($version && version_compare($version, self::REQUIRED_VERSION, '>='));
 
-        // Test the connection to the main connection.
-        $this->isready = @$this->connection->set("ping", 'ping', 1);
+        $this->isready = $this->is_connection_ready();
+    }
+
+    /**
+     * Confirm whether the connection is ready and usable.
+     *
+     * @return boolean
+     */
+    public function is_connection_ready() {
+        if (!@$this->connection->set("ping", 'ping', 1)) {
+            // Test the connection to the server.
+            return false;
+        }
+
+        if ($this->isshared) {
+            // There is a bug in libmemcached which means that it is not possible to purge the cache in a shared cache
+            // configuration.
+            // This issue currently affects:
+            // - memcached 1.4.23+ with php-memcached <= 2.2.0
+            // The following combinations are not affected:
+            // - memcached <= 1.4.22 with any version of php-memcached
+            // - any version of memcached with php-memcached >= 3.0.1
+
+
+            // This check is cheapest as it does not involve connecting to the server at all.
+            $safecombination = false;
+            $extension = new ReflectionExtension('memcached');
+            if ((version_compare($extension->getVersion(), '3.0.1') >= 0)) {
+                // This is php-memcached version >= 3.0.1 which is a safe combination.
+                $safecombination = true;
+            }
+
+            if (!$safecombination && (version_compare($this->connection->getVersion(), '1.4.22') <= 0)) {
+                // This is memcached server version <= 1.4.22 which is a safe combination.
+                $safecombination = true;
+            }
+
+            if (!$safecombination) {
+                // This is memcached 1.4.23+ and php-memcached < 3.0.1.
+                // The issue may have been resolved in a subsequent update to any of the three libraries.
+                // The only way to safely determine if the combination is safe is to call getAllKeys.
+                // A safe combination will return an array, whilst an affected combination will return false.
+                // This is the most expensive check.
+                if (!is_array($this->connection->getAllKeys())) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
     }
 
     /**
diff --git a/cache/stores/memcached/tests/memcached_test.php b/cache/stores/memcached/tests/memcached_test.php
index bef5cbe2704..db41269cd74 100644
--- a/cache/stores/memcached/tests/memcached_test.php
+++ b/cache/stores/memcached/tests/memcached_test.php
@@ -288,6 +288,10 @@ class cachestore_memcached_test extends cachestore_tests {
 
         $definition = cache_definition::load_adhoc(cache_store::MODE_APPLICATION, 'cachestore_memcached', 'phpunit_test');
         $cachestore = $this->create_test_cache_with_config($definition, array('isshared' => true));
+        if (!$cachestore->is_connection_ready()) {
+            $this->markTestSkipped('Could not test cachestore_memcached. Connection is not ready.');
+        }
+
         $connection = new Memcached(crc32(__METHOD__));
         $connection->addServers($this->get_servers(TEST_CACHESTORE_MEMCACHED_TESTSERVERS));
         $connection->setOptions(array(