On my Mandrake 9.1 box, I can do:
rm -f /home/flugh/.Mozilla/default/blahblah.slt/Cache/*
Obviously it's browser dependant. You need to just poke around your home directory until you find where your browser puts the cache files, then rm -f the files while at the commandline (or set the absolute path in the cookie, cache, etc cleaning script you are writing?).
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JBR