I have a good picture of AdS/CFT correspondence when the AdS space is given in terms of Global coordinates. In global coordinates, the AdS space is just a cylinder (up to a conformal factor) and gravity theory that is living within that cylinder has an equivalent description in terms of a CFT that can be considered to be living on the boundary of the cylinder. But I can also work in Poincare coordinates. So the CFT is living on the Poincare patch.
a) Now what is the relation between the CFT that is on the Poincare patch to the CFT that is on the complete boundary of the cylinder ?
b) Since Poincare patch is just a sub-region of the boundary of the cylinder, is it even reasonable to expect a consistent CFT will live on the Poincare patch, given a CFT on the complete space? Wouldn't the excitations from other parts of space-time make it impossible to consider a field theory defined just on a sub-region?