Domains on the same M-series machine are independent 'hardware' systems.
Here is what I've just found: 'A root pool cannot be exported on the local system. For recovery purposes, you can import a root pool when booted from the network or alternate media.' - ZFS Best Practices Guide - Siwiki
I may have to set a jumpstart server.
Finally I've used the way 'fugitive' suggested, and it's working well. Solaris 10 has been installed on the 2nd domain.
"I got to know that from SUN that in M5000 the DVD is hard coded to XSB00-0, so i had to work the other way around .. shutdown the domain 0 and assign XSB00-0 to domain1 and then do installation and put it back in domain 0 .. but that was possible because the server is not a prod box. :-)"