IE8 click Exit button, let cookie expired js

This is the background : the system is doing , there are two users with different permissions .
After a user logs in , click Exit , when the next user logs in, it will have a user has permissions , the permissions regardless of who logged in is large or small .
So now very tangled issue , especially to find a cookie can effectively allow expired js, in the IE8 browser to be easy , because I checked a js only available in IE6. Ask you to help it, sudden death
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document.cookie = yourCookieName + "=; path = /; expires = Thu, 01-Jan-70 00:00:01 GMT";
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seconds Shen ah == !

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No, this method is easy to say in IE6 , IE8 seems to die
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I understand, they are not cookie problem, but html file caching problem , although no one answered , or knot paste it
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did not know what was later to solve the same problems encountered here