Resolvers typically cache successful "does not exist" responses for no more than 1-3 hours. (And authoritative servers often have a lower negative TTL.) (There

Resolvers typically cache successful "does not exist" responses for no more than 1-3 hours. (And authoritative servers often have a lower negative TTL.) (There's a corner case related to DNSSEC that can make it go higher, but that's being worked on, and isn't relevant here.) In this situation, the nameservers were just down. I haven't done exhaustive research, but the resolvers I'm aware of cache that kind of thing for no more than 15 minutes.