Who owns Social Media in a Company – IT, Marketing, Legal, Sales, Agency?

With social media playing a major role in marketing now a days, it is imperative to know who owns the social media. There has been examples of conflict between the company & agency about the social media posting. Recently Chrysler fired its agency over the f-bomb tweet. For big companies, even the legal department also comes into picture. Also when the company hands out the contract to the agency, there should be clear road map about how to handle the conflicts.