Use DBCC DROPCLEANBUFFERS to test queries with a cold buffer cache without shutting down and restarting the server.
To drop clean buffers from the buffer pool, first use CHECKPOINT to produce a cold buffer cache. This forces all dirty pages for the current database to be written to disk and cleans the buffers. After you do this, you can issue DBCC DROPCLEANBUFFERS command to remove all buffers from the buffer pool.
Use DBCC FREEPROCCACHE to clear the plan cache carefully. Freeing the plan cache causes, for example, a stored procedure to be recompiled instead of reused from the cache. This can cause a sudden, temporary decrease in query performance. For each cleared cachestore in the plan cache, the SQL Server error log will contain the following informational message: "SQL Server has encountered %d occurrence(s) of cachestore flush for the '%s' cachestore (part of plan cache) due to 'DBCC FREEPROCCACHE' or 'DBCC FREESYSTEMCACHE' operations." This message is logged every five minutes as long as the cache is flushed within that time interval.