ARMv8-M Security Extensions (CMSE) is based on Trust-zone (TZ). Similar to other TZbased systems, there is a single Secure World and a single Non-Secure World. That means all code that is meant to be protected must mutually trust each other, as they all execute from the same shared single Secure World address space.
MIPS-VZ is based on hardware based CPU virtualization, which allows for multiple domains, each separate and protected from each other. This has the benefit that each piece of software that is meant to be protected need not trust other pieces of software, as each can have a private domain to itself. The MIPS-VZ architecture allows up to 255 separate domains, while particular CPU implementation might implement a lower number of domains.