Can even put it in redis too, if you have performance issues from looking for it in memory then you have probably have more users than google.

What if you have two servers, one in japan and one in central europe? Where do the sessions live?

With JWTs, you would only need to replicate your revocation list of the last X hours (X being your JWT default lifetime) and probably be in the megabytes for the total list. Easy to replicate that ever 5-10seconds to all your locations.