Você não pode porque o domínio não faz parte do conteúdo do cabeçalho do cookie enviado pelos clientes. Aqui está o trecho relevante da RFC 6265 sobre como o valor do cabeçalho Cookie é construído:
The user agent MUST use an algorithm equivalent to the following algorithm to compute the "cookie-string" from a cookie store and a request-uri:
Let cookie-list be the set of cookies from the cookie store that meets all of the following requirements : [...]
The user agent SHOULD sort the cookie-list in the following order : [...]
Update the last-access-time of each cookie in the cookie-list to the current date and time.
Serialize the cookie-list into a cookie-string by processing each cookie in the cookie-list in order:
Output the cookie's name, the %x3D ("=") character, and the cookie's value.
If there is an unprocessed cookie in the cookie-list, output the characters %x3B and %x20 ("; ").