So that the visitor of your website is not left with "temporary internet files" in memory in the cache of the browser, you need to purposely program the pages.
For .asp pages, the code must be :
Response.CacheControl = "no-cache"
Response.AddHeader "Pragma", "no-cache"
Response.Expires = -1
While for html, you only need to enter:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">