Domains and sub-domains will be treated as one site
While announcing the change, Google noted that domains and sub-domains won't be considered different under the new ranking mechanism.
This means that publishers won't be able to circumvent the latest restriction by offering similar kind of content through different sub-domains; they all will be considered as one website (mostly) and won't appear more than twice in search results.
Site diversity will generally treat subdomains as part of a root domain. IE: listings from subdomains and the root domain will all be considered from the same single site. However, subdomains are treated as separate sites for diversity purposes when deemed relevant to do so….