Can OF servers be in the same domain for the clustering

I am building an IM which can potentially support more than 100M users, Openfire cluster is one of my options. My questions are:

1. Can Openfire cluster support 100M register users? which probably means 10M concurrent users talking to each other at the same time for the cluster. I have many machines in the data center, just want to double check if Openfire itself can scale out that much with additional machine resources.

2. Will the openfire servers be in the same domain in the cluster?

Thanks,

Peter