> Correct but how do I know what my browser cache is doing
Look at request inspectors, log files, etc. Network behavior is easy to observe.
If you're an enterprise, typically, your employees have great connectivity to your corporate resources, so you're not going to get much out of prefilling the browser cache for them through desktop management software.
Make sure as much of your corporate intranet stuff as is reasonable counts as same domain for purposes of cache sharing, and standardize on a single version of your frontend libraries, etc, and you might actually get cache hits naturally. Standardizing frontend libraries is hard, but if shaving the couple of ms here and there is important, I'm sure you can find a way.
Now, maybe you've got a lot of work from home with terrible networks; that's pretty common today, or maybe you're work from the field and have had terrible networks forever. In that case, it might make sense to do something like wrap your web pages in electron where all the html/css/js is included and you only need to fetch data and you've got full control over the caching. Nobody on HN likes electron, but it would solve your enterprise problem. You might consider actually making an application, but that's unfashionable these days.
Of course, there's also the possibility of drastically slimming your pages down, etc, but that's a lot of work, so nobody wants to do that either.