Send some example code, if you can. Just a short snippet containing the code you're using to set the cookie.

Have you read the cookie specification? From that document:

    When searching the cookie list for valid cookies, a
    comparison of the domain attributes of the cookie is
    made with the Internet domain name of the host from
    which the URL will be fetched. If there is a tail match,
    then the cookie will go through path matching to see if
    it should be sent. "Tail matching" means that domain
    attribute is matched against the tail of the fully
    qualified domain name of the host. A domain attribute of
    "acme.com" would match host names "anvil.acme.com" as
    well as "shipping.crate.acme.com". 

    Only hosts within the specified domain can set a cookie
    for a domain and domains must have at least two (2) or
    three (3) periods in them to prevent domains of the form:
    ".com", ".edu", and "va.us". Any domain that fails within
    one of the seven special top level domains listed below
    only require two periods. Any other domain requires at
    least three. The seven special top level domains are:
    "COM", "EDU", "NET", "ORG", "GOV", "MIL", and "INT". 

    The default value of domain is the host name of the
    server which generated the cookie response.
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