Domain Mapping - 301 redirect

We are using the Domain Mapping plugin to map a particular domain (newdomain.com) to one of our sub-domains (sub.domain.com) - it works just fine.

However, we have a need to forward two other domains to newdomain.com via the DNS settings at the registrar - and in particular, a specific page within that site.

In other words, we want to redirect xyz.com and abc.com to newdomain.com/page1.

I'm wondering if anyone has had experience in doing something like this. Can I add a 301 redirect to the htaccess file that would handle this? Any example code you could offer? If the xyz.com domain is being redirected to newdomain.com at the DNS level, would the htaccess file even know that?

Thanks.