[rpastuszak]

I guess it really depends on the use case and the library.

I can imagine a tonne of WP sites referencing jQuery from the Google CDN, e.g.: https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.mi...

Looking at the headers the JS asset would be cached for 1 year.

[dathinab]

There are always a few exceptions.

But you also must consider that most people most times visit a small set of domains.

Which means that most times they will have jquery and similar cached even without cross domain caching.