one of the tricky things about the protocol is that a local cache may have gaps in it, and there is no negation in the filter

i've been thinking about posting an issue about this on nip-01 for a while, having the ability to prefix fields in the filter with a ! or so, to mean "no i don't want this one" would mean you could query local cache, then every ID you find you put in the filter with a negation and the upstream won't waste its time sending those events