Expires property
The Expires property specifies how much time remains before the cached page expires on the browser. If the user returns to a page before it expires, the buffered version is displayed
grammar
Response.Expires [= number]
parameter
number
How many minutes are left until expiration. Setting this parameter to 0 causes cached pages to expire immediately.
Comment
If this property is set multiple times on a page, the shortest time is used.
Applies to Response object
Response.expires=0 also means immediate expiration, but if the client and server are not in the same time zone or the client time is earlier than the time on the server, it cannot expire immediately. So use a negative number or use Response.ExpiresAbsolute=now()-1 to indicate immediate expiration, and response.expires=1 to indicate expiration after 1 minute.