Case Visibility in Portal

I have a requirement to restrict visibility to customers depending on there location ie.

Global can view all open cases

APAC can only see cases raised in location APAC

EMEA can only see EMEA cases

additionally it originally was set up Global as a parent account and the regional as a child account this initially this worked but now doesnt, is this best approached from  a ACL/ Role solution?

Thanks in advance 

M

Thank you in advance

Mike