MDS and DQS Duplication of Master Data

I'm confused about how MDS and DQS coexist.  MDS has domains, business rules, etc. to manage the master data in an organization.  DQS has a knowledge base that define domains, cleansing rules, business rules, etc. for cleansing, de-duplicating, etc. transactional data.  Where I'm confused is it appears that I have to have the domain exist in two (2) different areas.  What I'm looking for is one place to define the domains, cleansing rules, business rules, etc. that both MDS and DQS can both use thus having just one version of master data.  What am I missing?  What is the typical workflow used by each service?

Thanks,

Bigguy