Collision detection of off-screen objects (really far away objects...!)

Hi everyone,
I’ve been trying all day to solve this problem I have…

I’m currently developing a racing game. The player controls one car, and 7 cars are controlled by AI. The MovieClip which contains the race art is really big, like 4000px * 2000px, and in the AS I’m scaling it by 5. I also have a MovieClip for collision detection of the sides of the race (the grass). Let’s call this MovieClip mc_collision_detection. To detect collision with the grass, I run a hitTestPoint to each wheels of the car with mc_collision_detection.

The race runs great! Except for one thing…

When the AI cars are far away from my car, they don’t make the collision with mc_collision_detection! I think this is because the stage is too big, and the mc_collision_detection isn’t rendered far away from my car.

Is there a way to force the rendering of this MovieClip?
Did anyone encountered a problem like this before?