What's the use of multidomain NIS ?

Hi,
I was sent here by the NIS howto, hope this is the right place

I can't figure out why a nis client (ypbind) is able to bind itself to
more than one domain since it always queries the maps of one only (the
one returned by the domainname command).

I first thought that, when looking for an entry in a map, it would
first query its default domain server then the other(s) but it does
not. I then tried to create specific maps on each domain server, the
only visible one is... in the default domain.

If someone could explain, I'd be grateful

Thank you
the melon