In short: Less sharing - less contention. More sharing - more contention.

If you put 2 points on a line and call them 'no sharing' and 'share
everything', then
any system which allows you run on multiple cores and operate over
single domain (be it single memory or multiple standalone memories) is
lies somewhere in the middle.

You can pick a starting point from where you moving to that golden
point - from 'share everything' or from 'share nothing'. But it's no
doubt, no matter from where you started, you will always move towards
'golden' middle point.

-- 
Best regards,
Igor Stasenko AKA sig.