1. A method for caching web documents in two or more caches, the method comprising: for each query of a plurality of queries, where each query results in a plurality of web documents, each of the web documents of the resulting plurality of web documents having a corresponding tier score indicative of a position of the corresponding web document in the two or more caches, modifying tier scores of the resulting plurality of web documents by: determining an access penalty for each web document of the resulting plurality of web documents; determining a worst web document from the resulting plurality of web documents, the worst web document positioned in a cache of the two or more caches that has a highest access penalty relative to the access penalties for web documents of the resulting plurality of web documents other than the worst web document; modifying a tier score associated with the worst web document to indicate a higher priority cache, a higher priority cache having a lower access penalty relative to an access penalty for a lower priority cache; and modifying tier scores associated with web documents of the resulting plurality of web documents other than the worst web document to indicate a lower priority cache, a lower priority cache having a higher access penalty relative to an access penalty for a higher priority cache; wherein said modifying a tier score associated with the worst web document to indicate a higher priority cache further comprises: modifying the tier score associated with the worst web document to indicate a lower priority cache by an amount that is calculated using at least one of: a duration of time since the tier score associated with the worst web document was previously modified; and a cumulative deferred decrement of the tier score associated with the worst web document, wherein the cumulative deferred decrement is indicative of previous deferred modifications of the tier score associated with the worst web document indicating a lower priority cache.