Recently, research on Information-Centric Networking (ICN) has flourished, which attempts to shift from the current host-oriented Internet architecture to an information-oriented one. The built-in caching capability is a typical feature of ICN. In this paper, in order to fully exploit the built-in caching capability of ICN, we propose a collaborative in-network caching scheme with Content-space Partitioning and Hash-Routing, which is named as CPHR. By intelligently partitioning the content space and assigning partitions to caches, CPHR is able to constrain the path stretch incurred by hash-routing. We formulate the problem of assigning partitions to caches into an optimization problem of maximizing the overall hit ratio and propose a heuristic algorithm to solve it. We also formulate the partitioning proportion problem into a min-max linear optimization problem to balance cache workloads. By simulations with both the characteristics of real Internet traffic and traces of peer-to-peer (P2P) traffic, we show the necessity of collaborative caching since the en-route caching mode cannot yield a considerable overall hit ratio with practical cache size. It is shown as well that CPHR can significantly increase the overall hit ratio by up to about 100% with the practical cache policy Least Recently Used (LRU) while the overhead incurred is acceptable in terms of propagation latency and load on links.