Remove all clean buffers from the buffer pool.
Syntax
      DBCC DROPCLEANBUFFERS [WITH NO_INFOMSGS]
Key:
   WITH NO_INFOMSGS - Suppress all information messages.
This command is useful to test queries with a cold buffer cache without shutting down and restarting the server.
To produce a 'cold' buffer cache with all dirty pages written to disk, first use CHECKPOINT.
# Why can't I ease your doubtful mind, and melt your cold, cold heart # ~ Hank Williams
Related:
 CHECKPOINT
  DBCC FREE... CACHE  
Equivalent Oracle command:  ALTER SYSTEM FLUSH SHARED POOL