Hi,
the destination URL can point to any domain, while on the source URL we just take the REQUEST_URI part.
Anyway, for your problem, if you still can control the old domain, you can redirect every call to new domain. There's at least two way to do this.
First one is using Apache rewrite URL. In this way you should be able to redirect any call to the same on new domain.
A simplest way is (if you have Joomla and ReDJ on the OLD domain) to use the new 1.3.2 feature. You can redirect ANY error to a single URL (e.g. the new homepage).
If you need more help, please, don't esitate to ask me.
Regards,
Luigi