well, that's a cache invalidation issue. Any data that's cached, by definition may not be the freshest version, unless you've implemented a very nice write-through situation. If you'd like multiple requests to share an in-memory-only cache, potentially using write-through, then yes that deals with synchronization issues. I wouldn't characterize them as super-tough synchronization issues and you certainly won't have a "blocking IO" problem with an in-memory system.

If you want to write your own caching server, fine, use node.js. But now you're writing your own cache server, you've found some problem that memcached, redis, etc. all do not solve. Is this an everyday use case ?