A while back, I wrote a simple PowerShell script that will clear the cache on a SCCM client machine (I will post this script for your reference at the end of this blog).
I mostly used this script during a large Task Sequences (ie. during a build and capture task sequence that installs a lot of software), since the cache would fill completely and then fail the Task Sequences (it appears that SCCM will not override any items in cache during the task sequence). This never presented an issue since I always ran the script directly from the Distribution Point.