When you say multiple JIRA I assume you mean multiple JIRA projects. Accessing multiple projects via a classic (chart) board is not possible, this was one of the main reasons Rapid Boards were added.
You can do what you ask using a Rapid Board in v 5.8.7: https://confluence.atlassian.com/display/GH058/Using+the+Rapid+Board
The JQL behind the filter can be used to reference multiple projects, e.g.
Project in (PRJ1, PRJ2, PRJ3)
Does that work for you?
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