Q: Do I need to inform my target journal that the study was presented at a domestic conference?

It is quite common for researchers to present their preliminary findings at a conference before they submit their manuscript to a journal. Submitting intermediate data from your research to a domestic conference does not preclude submission to a journal. However, it is best practice to inform the journal editor that you have submitted preliminary data at a conference. Also, you need to ensure that the title of your manuscript is slightly different from that of the conference abstract. and that the journal paper has at least 30% original data that was not presented at the conference. 

Related reading:

• Is it acceptable to present research at a conference before it is accepted by a journal?
• Is it acceptable to make a conference presentation before my manuscript is published?
• Is it acceptable to publish a conference abstract and an article based on it in two different journals?