Programmable switches have been widely used to design network monitoring solutions that operate in the fast data-plane level, e.g., detecting heavy hitters, super-spreaders, computing flow size distributions and their entropy. Existing works assume packets access the same memory region in a switch. However, high-speed ASIC switches deploy multiple packet processing pipes, each equipped with its own independent memory. In this work, we first quantify the accuracy degradation due to splitting a monitoring data structure across multiple pipes (e.g., up to 3000x worse flow-size estimation average error). We then present PipeCache, a system that adapts existing data-plane mechanisms to multi-pipe switches by storing monitoring information for a traffic class into a single pipe. PipeCache stores monitoring information into a cache and piggybacks this information onto existing data packets to the correct pipe. Our implementation shows a 2-20x memory reduction to achieve an accuracy similar to single-pipe deployments.