When one cooks meat in a dairy pot (or vice versa), if the pot has been used in the past 24 hours with hot dairy, the meat that was cooked in it is biblically prohibited, and the pot needs to be koshered. If the pot was not used in the past 24 hours, it is forbidden to cook in it initially, but after the fact the food would be permitted. The pot would still need to be koshered. In this case the pot really does not have any absorbed taste that is forbidden, because any taste absorbed in the pot is not considered edible once it is more than twenty-four hours old. One could theoretically still use the pot for pareve, but it is proper to be stringent and kosher it prior to further use (רמ”א יו”ד פז:ו).