The Internet plays an increasing role in content dissemination as user-generated contents have exploded recently. Cache servers have been deployed to bypass bottlenecks in the network so that contents can be delivered to end users more efficiently. With caches becoming more embedded in the networks, emerging threats follow naturally. A cache pollution attack is one of the most serious threats on caching networks including the current Internet and emerging caching networks such as Content Centric Networking (CCN). In this paper, we propose a detection approach against cache pollution attacks using randomness checks of a matrix. We apply an effective filtering approach and a statistical sequential analysis for detecting low-rate attacks. The results of our experiments show that our approach can detect a cache pollution attack with attack rate of only a few percent of the overall rate.