 domain can't work

I just want all website '**.mujishi.com' can user cookie  and I wrote the following:
            ipCookie('token', token, {expires: 20},{domain:'.mujishi.com'});
and I log in the a.mujishi.com and I can see the cookie in chrome-resources but if I open b.mujishi.com ,I can't get the cookie ,I'm wondering why?Did I write wrong or something?
