denisl - 5:20 pm on May 23, 2012 (gmt 0)
The following function works for me (borrowed from somewhere)- I call the function in the body tag of the thank you page. Deletes cookies on page load without having to name them.
var new_date = new Date()
new_date = new_date.toGMTString()
var thecookie = document.cookie.split(";")
for (var i = 0;i < thecookie.length;i++)
document.cookie = thecookie[i] + "=; expires=Thu, 01-Jan-70 00:00:01 GMT; path=/; domain=.domain.com;";