When I have worked with scaling Scrum over several teams (up to 10 in parallell), I have strived to strengthen the same processes that gives traction to a single team.

Alistair Cockburn compiles this beautifully in his Software engineering in 21:st century

People issues determining a projects speed

• Can they easily detect something needs attention? (Good at Looking Around)
• Will they care enough to do something about it? (Pride-in-work; Amicability)
• Can they effectively pass along the information?  (Proximity; face-to-face)