cache flush

[antonio anselmi]

I set my network to use opendns.  I setup a very
restrictive option so it blocked even all games sites.  Yet for many
hours (at least), I could still get games.

Then, I rebooted the nodes and immediately games were blocked.

So I did the reverse and unblocked games and see the same problem:
games stayed blocked for many hours (at least) but were immediately
unblocked when I rebooted the nodes.

There seems to be some long-term caching going on?
How can I periodically flush the cache?

thanks for your help