Cache invalidation is an important issue in mobile caching and has received much attention by researchers. However most existing studies on cache invalidation strategies are limited to cellular wireless networks in which the mobile terminals can communicate with the base stations directly. In this paper, we address the seldom studied issue of cache invalidation in mobile ad hoc networks (MANETs), where the use of multi-hop communications poses serious challenges. We propose three cache invalidation strategies for MANETs. The three methods, namely pull on demand (POD), modified amnesic terminals (MAT) and pull-based amnesic terminals (PAT) are adapted from Barbara and Imielinski's classic cache invalidation schemes to handle the special requirements of MANETs. Both analytical results as well as simulation experiments are used to examine the performance of these three schemes, and it is shown that PAT provides the best overall performance.