The Answer lies in the definition

What you define the responsibility to be, ultimately gives you the boundary.

Example:

I have a component that has the responsibility of displaying invoices -> in this case, if I started to add anything more then I'm breaking the principle.

If on the other hand if I said responsibility of handling invoices -> adding multiple smaller functions (eg printing Invoice, updating Invoice) all are within that boundary.

However if that module started to handle any functionality outside of invoices, then it would be outside of that boundary.