Finding orphan records

I'm trying to find/delete all records in table A that are no longer
referenced by tables B or C. There are about 4 million records in table A,
and several hundred million in tables B and C.

Is there something more efficient than:

select address_key, address from addresses where ( not exists(select 1 from
B where BField=addresses.address_key limit 1) ) and ( not exists(select 1
from C where CField=addresses.address_key limit 1) )

Of course, all fields above are indexed.

There are foreign key references in B and C to A. Is there some way to
safely leverage that?

Wes