copying *.deb files into /var/cache/apt/archives

[Adam Funk]

Let's say I've just carried out some big upgrades, or even a
dist-upgrade, on one computer on a LAN, & I want to do the same on
another one.  Or I've done it on my computer at the office with a much
faster internet connection, & I want to carry all the *.deb files home
on a USB drive to save downloading time.

I tried copying the new *.deb files from one machine's
/var/cache/apt/archives directory into the same place on another
machine, but neither aptitude nor the GUI update manager recognizes
them; they try to download the packages again.  What do I need to do
to make them re-index the archives directory or otherwise take notice
of what's been copied in there?

Thanks,
Adam