Will an IIS reset force cached items to be resent?

When you do an IISReset the IIS cache will be cleared and then will start to be rebuilt after it starts back up as client requests come in. If you update a file then the older cached file will become stale and IIS will serve the updated file and update the cache with the new file.

IISReset (although harsh) will clear the IIS cache but it won't do anything with local caches in proxies or clients. Maybe you've just got the terminology mixed up a bit, but there isn't any concept of "resent" when it comes to caching. It's all request based. If a client requests something and it's found in a cache then it'll get served from the cache. You'll need to force content expiration on your files if you will be maintaining the same filenames.

No, client caching is based on content expiration time.