What to do with patches that should go upstream?

Hi,

I'd like to know what's the best practice to follow when one discovers
that a change that's been applied on the current branch, has to
actually go upstream. For example, in the following figure,

     A
-O---O-+
        \        A'  B'
-O---O---O---O---O---O---O W
            /
  -O----O--+

W is the current working branch. But there are commits A' and B' which
should go upstream. What I wanted to know is the next step from here.

1) Do I switch to A and B, and then cherry pick the commits A' and B'?
2) If I send the patch out to include in upstream, wouldn't it
conflict the next time I happen to merge from A or B?

Please suggest.

-- 
:J