You should not use
it as top level domain, which is an official TLD on the internet.
Some programs will try to lookup athlon64.localdomain.it in the official DNS. Of course this lookup will fail.
Code:
$ host athlon64.localdomain.it
Host athlon64.localdomain.it not found: 3(NXDOMAIN)
Instead use a TLD that doesn't exist e.g.
xit
It could be that some configuration files still have your old
domain_not_set.invalid domain name in it.