DynamoDB provides a secondary layer of Availability in the form of Cross Region replication (Global Tables)

With Global Tables, DynamoDB becomes a Multi-Master database and

Data is replicated asynchrounously (via DynamoDB Streams that are automatically created as so as you create the Global Table) in tables located in different regions and each table contains the same set of data ( not like memcacheD nodes which have different partitions of the data).

Besides increasing availability in case of regional outage, Global Tables also reduce latency because your user will access data from the closest located table replica (data locality)