Query Strings

Most browsers these days will see a URL with a different query string as a different file and download a fresh copy. Most CDN’s even support and recommend this.
<link rel="stylesheet" href="style.css?v=3.4.1">

Make small change? Change it to:
<link rel="stylesheet" href="style.css?v=3.4.2">
 

Fuente: https://css-tricks.com/strategies-for-cache-busting-css/