DBCC commands to free several SQL Server memory caches:
Releases all unused cache entries from all caches. The SQL Server 2005 Database Engine proactively cleans up unused cache entries in the background to make memory available for current entries.
Flushes the distributed query connection cache used by distributed queries against an instance of Microsoft SQL Server.
Removes all elements from the procedure cache.
Reference : Pinal Dave (http://blog.SQLAuthority.com) ,BOL