How to implement cache invalidation using PHP using the last modification time of a file?

All kind time of day!
If incorrectly asked a question, then please correct.
The essence of the question is appropriate way of the cache for the project.
Goal: to organize the update of the cache in the browser after the update file using PHP.
Updating the cache CSS and JS - that's understandable. I deduce the date of the last modification of the file, as parameter after the sign "?". What about the HTML (images, for example)?
The first thing that comes to mindis subject to some conditions (for example, to the page file, inspect the file for modification) to send to the server headers for caching settings. But, then you will need to store a variable for each user's modification time (this is nonsense).

Tell me how and just cache the page?
PS could do and setting a date of last page update in the headlines, after the upgrade, but the project is given to the customer under CMS, this option is not roll yet.
June 5th 19 at 21:27

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