Disabling Debian/Ubuntu apt archives

Hi, Linux distros using the apt package management system tend to cache downloaded packages in /var/cache/apt/archives/ If you have many very similar machines set up, then you'll almost certainly have a HTTP proxy cache setup for them to retrieve packages through, to reduce huge duplication of downloads. This essentially obsoletes the /var/cache/apt/archives, though. And when you're running dozens of virtual machines, it'd be nice to avoid storing all these duplicate files. What's the right way to disable it? I see I can adjust the max size and age via the APT::Archives::Max{Age,Size} parameters, but what about just turning it off altogether? Cheers, Toby