Here is a small info on the Multi-level caching
A multilevel cache spreads the cached data contents across several servers across the network.
- The top level caching server holds the most commonly accessed pages, and the lowest-level caching server holds the least commonly accessed pages.
- The various levels combine in a network of cache servers called a Web caching mesh.
- The caches communicate among themselves, using HTTP and special cache-coordination protocols, to divide the contents appropriately and maintain consistency among the servers