clarifications about ARCACHE bits in AXI4

the definition  of ARCACHE[3] is mentioned below. and also it is used in identifying the write back and write through memory type encoding in AXI4. 

as this bit is used in memory type encoding , in which cases the below definition will be used. why there are two definitions for the same signal ?

ARCACHE[3] Other Allocate When asserted, the transaction must be looked up in a cache because it could have been allocated in the cache by another transaction, either a write transaction or a transaction from another master. The transaction must also be looked up in a cache if ARCACHE[2] is asserted. When deasserted, if ARCACHE[2] is also deasserted, then the transaction does not need to be looked up in a cache.

could you please clarify ?