sharing /var/cache between two installations of debian?

[Aldebaran <aldebaran@cinci.rr.com>]

I am using apt-cacher and apt-build.  apt-cacher keeps it's stash 
in /var/cache/apt-cacher/ and apt-build keeps it's stash 
in /var/cache/apt-build/repository.

I have two debians installed.  Deb1 and Deb2 on hda1 and hda2.
I only use one at a time.  For instance, I am using Deb1 currently, I make 
backups of deb1 and at some point verify that the backups work by doing a net 
install of debian to deb2 and restoring my backup to deb2.  At which time I 
will switch and use deb2 for a while.  During that time deb1 is unused.

I want to both to use the same /var/cache partition.  /var/cache has its own 
partition.  I already share /tmp and swap.  Is there anything in /var/cache, 
or is there anything that could be in /var/cache that would cause problems if 
it was shared in this way?  I see that debconf has stuff here.  Is there any 
likely problem sharing this partition in this way? I don't really know what I 
am doing which is why I am asking.  I don't really know what debconf does, is 
it going to be a problem?

Is there a better way?

ls /var/cache:
apache
apt
apt-build
apt-cacher
apt-listbugs
debconf
dictionaries-common
fonts
gnome-system-tools
locate
lost+found
man
man2html
setup-tool-backends