First you have to add in your named.conf the section about domain2.com. Then since you're going to replicate your domain1.com, just copy the zone file of domain1 to a new file that will be the zone file of domain2 and change any occurence of "domain1" in it to "domain2". You can do it automatically with sed"
Code:
sed 's/domain1/domain2/g zone.domain1 > zone.domain2
The only problem you'll have, is the reverse lookup, since you cannot have an IP address that resolves in 2 different hosts