Note: DNS already has a cache invalidation mechanism in the TTL of the DNS record. I think you’d be well advised to simply use that; i.e. just look up the doma

Note: DNS already has a cache invalidation mechanism in the TTL of the DNS record. I think you’d be well advised to simply use that; i.e. just look up the domain every time, and let the DNS TTL be your caching mechanism for domain lookups. (You’d also probably better make sure your DNS resolver uses DNSSEC validation, and that your DNS resolving code path requests it by default.)