Multiple data centres

I have a scenario where we have an on-site data centre hosting our web application.

We have limited options for expanding this data centre and so we're looking at our options for a second data centre, while maintaining our existing one and linking the two.

I'd like to add at least a caching layer to this web application. In a perfect world distributing the cache across the data centres.

Can Membase help with this scenario and what are the pitfalls to watch out for?