Abyssal Knight, using additional flags. I used to do similar things like this (the code isn't complete, but it illustrates the principle):

-- table storing region names and visit flags
region_table =
{
  {name = 'NAME_OF_THE_FIRST_REGION', visited = 0},
  {name = 'NAME_OF_THE_SECOND_REGION', visited = 0},
  ...
};

-- initialization function
function RegionInit()
  for i, region in region_table do
    Trigger(REGION_ENTER_AND_STOP_TRIGGER,  region.name, 'RegionVisit');
  end
end

-- unified visit function
function RegionVisit(hero)
  -- check which region we are in
  for i, region in region_table do
    if(IsObjectInRegion(hero, region.name)) then
      Trigger(REGION_ENTER_AND_STOP_TRIGGER, region.name, nil);
      region.visited = 1;
      -- here you can do what you need, depending on the region number (variable i is the number in the region_table table)
    end
  end
end

-- returns true if the region with the name name has been visited
function IsRegionVisited(name)
  for i, region in region_table do
    if((region.name == name) and (region.visited == 1)) then
      return true
    end
  end
  return nil
end