reply for reserved TLD's

[Sonic]

Hello,

What is considered the best reply from a local cache to avoid traffic
to the root servers for domains that are reserved (for local use etc.,
such as .home, .corp) or those you wish to block?
Is always_nxdomain better than always_refuse? Is there an even better reply?
Does one or the other prevent the querying system from attempting to
query other caches, that may or may not be blocked?

Thank you,
Chris