In order to do this I would use a helper entity. When opening the page create a new object of this entity.
Put the listview in a dataview of this helper entity and place the selector for the region in the dataview.
Use an on change microflow so that when the region is changed, you retrieve all cities in this region and associate them to the helper entity. Then refresh the helper entity, in order to refresh the page.
Set the listview to only show citites associated with the helper entity. If you want you can associate all cities with the helper upon opening the page, to show all available cities.
Hope this helps.