You can also try running a white snowy screen at high contrast for several hours. You can achieve this by selecting the antenna input, assuming you can use it disconnected. There are also some very good calibration discs like the ones Scott referred to and the Disney WOW Blu-Ray, which not only offer effective screen washers, but also have test patterns you can use to help keep the performance of your set at it's best. A properly adjusted plasma is less likely to experience stubborn IR, as long as you don't display static images for long viewing periods. I've also found that most built in anti image features like the pixel orbiter and scrolling bar, aren't that helpful.
Ian