page_cache_maximum_age wrongly set
Either you don't need, or you can't:

If this was translated to HTTP header, and browser "knows" not to ask for the page again, nothing you would try to do about it will have any effect, because browser simply won't contact your server anyway, so it will not download any remedy you might try.

If it affected only server-side systems, tuning it down and clearing caches should be enough already, and server shouldn't send "304 Not Modified" to your clients.

Hard to tell which case is it without knowing your caching setup, but I'm afraid "fix it and wait" is the only way either way.

Unless, for some reason, you can identify uncached JS file included on affected pages. This would be a bug, so I don't expect it to happen, but if, it might be a bug you could use - ask for it on Stack Overflow, then, as this is much less Drupal-related.

If your front page isn't cached that way, you can alter all affected links. It will not help people having issues with bookmarked pages, but it will direct regular users to current content.