Fragment Caching - happening twice

I am using fragment caching - the cache gets stored under RAILS_ROOT/ tmp/cache/www.mysite.com but if I go to http://mysite.com (no www) then a *second* cache gets stored at RAILS_ROOT/tmp/cache/mysite.com - from this point on the cache is hit but I end up with 2X the DB hits I really need. How can I avoid this?

Also where can I configure the fragment cache location - I was thinking of putting it under RAILS_ROOT/public

Thanks