Everything

Like many other elements of Mage 20th Anniversary Edition, the reality-zones concept is optional:

• Your group could use it to determine the sorts of Effects and practices that are coincidental or vulgar;

• You might simply ignore it and assume that the entire world operates under Technocratic Reality;

• …or you could deepen the game and allow your players to change their world by creating paradigm shifts that, in turn, alter capital-R Reality and literally change the rules in their favor.

The choice between those options, ultimately, is yours.