global is an argument specifically for the "Memory" (CHI::Driver::Memory) driver. If you're using a different driver then you'd consult the documentation for the custom options that particular implementer uses (i.e. CHI::Driver::File for the relevant options for that module).

Edit: Just to expound on this, the docs for CHI show the common constructor options that are available irrespective(*) of the driver being used; anything specific to a given driver module would be documented with the driver module.

(*) I'm not really familiar with CHI so conceivably there could be some options that are incompatible with some drivers but I'm not aware if that's actually the case; the documentation for the individual drivers would say for sure were that the case.