Data sets created in a Dashboard are specific to said Dashboard. They cannot be reused in separate instances.
However, you can use a single Data Query data set in multiple Dashboards:
- create a template in Data Query using the dimensions, metrics and segments you need
- In the Dashboards Manager interface, click the arrow next to the "New" button in the "Data" menu and select "Import a Data Query template" from the pop-under
- Rinse and repeat for every Dashboard that needs this data
More information on this here: Importing Data Query templates