1984 Cent Reverse

I don't believe that's doubling at all. It appears to be where the coin came into contact with something dirty - the beginning of wear. The line at the top of the devices that is being misinterpreted as a separation line of a doubled die is actually just a high-point dirt line.

The reverse used during that time doesn't have completely flat tops to the letters - they are sort of curved over at the top and when they are rubbed the area of wear can be very small - just a thin line.