moving apt's cache

[Ross Boylan <RossBoylan@stanfordalumni.org>]

Currently, apt's cache is in /usr/var/cache/apt.  I would like to move
that back to /var/cache/apt, thanks to new disk space.

I recall some problems with this when I originally moved it, I think
because some other files had pointers to the location.  That was quite
awhile ago.  Does anybody know if it is safe to make the switch simply
by editing 
Dir {
	Cache "/usr/var/cache/apt";
};
in apt.conf and mv'ing the files?

By "problems" I mean that apt starts downloading all the debs again,
seemingly not recognizing that it has them.

Thanks.