Response.Cookies(x).Domain?

I am looking for a way to delete (expire) all the cookies that we've ever written to the user's machine. I have found several scripts, however I have come across one "gotcha."

The scripts I have found all look something like this:

response.buffer = "true"
dim x
for each x in Request.Cookies
Response.Cookies(x) = "must be something"
Response.Cookies(x).Expires = "January 1, 1999"
next

One cookie gets set like this:

Response.Cookies(x).Domain = ".henryschein.com"

so that we can retrieve it from 'www.henryschein.com' and
'info.henryschein.com'

The problem is that the script above does not delete it.

Anyone have any idea why this is?? Anyone have a script that properly deletes ALL the cookies that you've ever written to the user's machine?