the problem is, global variables are actually "global". There are none that are scoped to just that sheet/layout. Global vars can be made anywhere in the project, what sheet they are declared on is arbitrary. what you are describing is a local variable.
if you want those variables to be confined to just that event sheet, place all the events inside of a group, then drag all the variables to be at the top of the group. then each of the variables will be reinitialized each time you run the layout.