Coverage question

For the question shown below, should this be understood to write a cover group for vector bit toggling? My question is how should I write coverage for the below?

Write coverage for a 4 bit address, all address bits have seen 0 ->1 once

bit [3:0] addr;
covergroup cg;
coverpoint addr {
bins sa = (0=>1);
}
endgroup

Please help me how to understand if all bits have toggled.
Thanks in advance.

In reply to sk7799:

https://verificationacademy.com/forums/coverage/functional-coverage-check-each-bit-toggled-or-not-memory#reply-88152