What exactly do you want to clear from the cache = there are a number of specific calls that can be used to clear different parts of the case.

For example - to JUST clear the cache for a specific user:
DotNetNuke.Common.Utilities.DataCache.ClearUserCache(thisPortalid, activeUser.Username);

To clear the entire cache:
DotNetNuke.Common.Utilities.DataCache.ClearCache();

I would ideally make sure you only clear as much of the cache as you really need - excessive cache clearing could be very detrimental to your site performance.

Westa