Fragment Caching - happening twice

I am using fragment caching - the cache gets stored under RAILS_ROOT/
tmp/cache/ but if I go to (no www)
then a second cache gets stored at RAILS_ROOT/tmp/cache/ -
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