isc trust anchor

[sami's strat]

If I have two domains, say a.us and b.com

a.us is (dnssec) signed and the parent domain has a copy of the DS keys.

Is there a way to have host.b.com run dnssec aware queries against a.us?

I was thinking of setting up and using the ISC trust anchor with both
domains.  Would that work?  Are there better ways to have a .com
domain query a fully signed and operational .us domain?

Thanks in advance.