APEX

I have a long running query which populates a region. Each user can enter their own selection criteria (i.e. search by name, ssn or address, etc..). So I set this region up to "Cache By User" with a timeout after 10seconds.

My problem is how do I clear the cache for just A user. When I look in the APEX_APPLICATION_CACHING view, I can see the entries for each user.
Using APEX_UTIL.PURGE_REGIONS_BY_APP() seems to delete everyone from application cache.

So my quesiton is, is there a PURGE_REGIONS_BY_USER api some where ? Or something that lets me purge the region cache for just one user ?

Thanks!