While the US is dismissive of North Korea's proposed "joint investigation" into the Sony hack, according to a New York Times report, the Obama administration has reached out to China for help in "blocking North Korea's ability to launch cyberattacks."
It's an interesting development, as the US have linked Chinese government hackers to multiple attacks (including a recent attack on the US Postal Service). But China is also a key provider of North Korea's internet access, although the US doesn't seem to believe China is involved in the recent Sony Pictures incident. According to The New York Times, US officials see this as a chance to work with China on "establish 'rules of the road' for acceptable behavior in cyberspace." The Chinese have reportedly not responded.
A lot of questions have centered around what Obama means by a "proportional" response to the Sony hack. The report mentions a few options being considered, including new economic sanctions or so-called "information operations" directed at the general North Korean population. It sounds like a cyberattack against North Korean military facilities is not in the cards, however: "For now, the White House appears to have declined to consider what one Defense Department official termed 'a demonstration strike' in cyberspace."
Remember: Cyberwar is bullshit.