how to downgrade libc6?

[Tomasz Wzietek <linuxguy@myrealbox.com>]

hello,

i'm running potato r3. i upgraded libc6 2.1.3-18 to 2.2.2-4 
(as well as -dev & a couple of other packages along with 
it) from the "testing" tree. what's the best and quickest 
way to restore the original ver?

i tried 'apt-get install libc6' from the "stable" tree but 
it complains that it's already up-to-date. i also 
tried 'apt-get --reinstall install libc6' but it says that 
it "cannot download file". what gives?

i obviously don't want to do 'apt-get remove libc6' ;)

any suggestions please? thanks in advance!