MD and PA have tax reciprocity for W2 income. That means that PA residents are not subject to MD income tax on their W2 earnings. You should file MD Form MW507 with your MD employers so that MD taxes will not be withheld from your pay.
Here's a link to that form:
https://www.marylandtaxes.gov/forms/current_forms/mw507.pdf
In order to obtain a refund of the incorrectly withheld MD taxes, submit a non-resident MD tax return on which you show the MD withholding but allocate zero income to MD.
You are not entitled to an "other state credit" on your PA return because in fact you owe zero in MD taxes.
Note: my answer assumes that you have no MD-source income other than from your jobs.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
