Must one clean/wash both hands if only one hand touched a dirty area?[1]
Some Poskim[2] rule one is only required to clean/wash the hand that touched the dirty area and not the other hand. Other Poskim[3] rule one is required to wash both hands [by actions that bring an evil spirit[4]]. Practically the main opinion follows the lenient opinion although one who is stringent [regarding those actions that bring the evil spirit], is blessed.
[1] Kaf Hachaim 4:86
[2] Chayeh Adam 40:18; Admur in Seder Netilas Yadayim 17 regarding one who touched a covered area during a meal that he must only wash that hand [However Tzaruch Iyun if this can be used as a source as perhaps regarding removing the Ruach Raah washing both hands is required.]; Other Poskim listed in Kaf Hachaim ibid
[3] Yifei Laleiv 1:27; Leiv Chaim 2:7; There he concludes that so rules the Shlah Hakadosh and so is the custom of the world.
[4] See Halacha 1. All actions that are not listed there are not known to bring an evil spirit and hence would not require the cleaning of both hands according to any opinion.