Not sure, there is already a (data) valid answer to this, but maybe this gives you a clue:
if you +1 something, Google should normally know, who you are, what you searched for and how you reached the page.
So in a first layer - the +1 should only be really important for that specific page and its verbatim.
Given that a site generates a lot of +1s for different pages in time and in a specific topic (soccer shoes, basketball shoes, and so on) the positive ranking of those subpage could/should be inherited by the upper roots...and finally by the root domain.
But that's just my assumption on how I expect Google to handle this - there is no real data available out there yet...
