Hi,
Prior to clear corrupt definitions, have you checked definitions are corrupted or not?
How to determine if virus definitions of Symantec Endpoint Protection client (SEP) 11 or 12 Small Business Edition, are corrupted
http://www.symantec.com/docs/TECH97677
If yes, then go through the following articles.
How to clear out corrupted definitions for a Symantec Endpoint Protection Client manually
http://www.symantec.com/docs/TECH103176
How to clear out definitions for a Symantec Endpoint Protection 12.1 client manually
http://www.symantec.com/business/support/index?page=content&id=HOWTO59193