BIND's separation of authoritative (zone) and nonauthoritiative (cache) data has always been somewhat weak, and pollution of the former via the latter has been known to occur. One way to prevent this, as well as to save memory on servers carrying a lot of authoritative data (e.g., root servers) is to make such servers ``nonrecursive.'' This can be achieved via the directive
options no-recursion
in the bootfile. A server with this option enabled will not attempt to fetch data to help answer queries -- if you ask it for data it does not have, it will send you a referral to a more authoritative server or, if it is itself authoritative for the zone of the query, it will send you an negative answer.
A nonrecursive server can be named in an NS RR but it cannot be listed in the resolv.conf file.