close window delete cookies

[wxdqz]

Hi All,
I need a way to detect that the user has clicked the close button ( X ) and run a script which can clear cookies. I already know how to clear the cookies (using vbscript response.cookies) but I don't know how to run the clearcookies script if the user presses the the close button

such as

if document.closebutton
{

document.location.href="clearcookies.asp";
}

can anybody help me out

many thanks

Marko