如何理解ARM架构中的Coherence order？

各位专家：

     最近在看ARM架构memory model方面的资料对Coherence order不知如何理解，麻烦各位专家解释一下，谢谢！

1. Coherent     

     Data accesses from a set of observers to a byte in memory are coherent if accesses to that byte in memory by the members of that set of observers are consistent with there being a single total order of all writes to that byte in memory by all members of the set of observers. This single total order of all writes to that memory location is the coherence order for that byte in memory.

2. 其外，还有一个问题就是观察者顺序和程序的顺序是一样的意思吗？