How to get all the availability domains?

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I need to get all the mount targets in the tenancy. There will be 2 mount targets per availability domain. 

Do querying with each region & root compartment is the best way to get all the availability domains?

https://identity.eu-frankfurt-1.oraclecloud.com/20160918/availabilityDomains?compartmentId=ocid1.tenancy.oc1..abcdefghi

https://identity.us-ashburn-1.oraclecloud.com/20160918/availabilityDomains?compartmentId=ocid1.tenancy.oc1..abcdefghi

https://identity.ca-toronto-1.oraclecloud.com/20160918/availabilityDomains?compartmentId=ocid1.tenancy.oc1..abcdefghi

Please let me know your inputs/suggestions.