about writing to GIC ICC_AP0Rn and ICC_AP1Rn

Dear arm experts：

    The GICv3 spec says that An ISB is not required between each write to ICC_AP0R<n>_EL1, Secure ICC_AP1R<n>_EL1, and Non-secure ICC_AP1R<n>_EL1. 

    I'm not sure if any ISB is needed after writing ICC_AP0Rn and before ICC_AP1Rn. or does it mean we just need one ISB after writing to all ICC_AP0Rn and ICC_AP1Rn? 

Thanks