First is to clear the cache drive settings in the TMG console, restart service, then delete the cache files on the server but it simply removes the whole cache information you have built along the time since you have enabled it…
When the deletion and cleaning is finished you need to re-enable the cache again and your users will need to fill the cache from scratch. All this operations can also be done by a script.
Another way, that might be more effective, is to use the CacheDirPack from the TMG 2010SDK . The SDK has other cool features as well but lets focus for now on caching issues.
(don’t forget after installing to move the .exe file to your TMG installation directory, it doesn’t start when you run it from where it is default installed)
With this tool you can select obsolete items per website and mark them as obsolete. After you still need to restart the firewall services to clear the RAM cache.
Tools for TMG including the TMG CacheDir tool can be downloaded from the Microsoft Download site: