This is my extracted onChange function for what to do when the post_type value is changed in a Gutenberg block. I have two dependent selectControl elements which should have their options updated. At this time, I can update the value of the dependent controls, but I can't figure how to change the list of options.

block.js

function onChangePostType( select_id, value, props, setAttributes ) {
	const data = {
		action: 'my_ajax_action',
		security: 'my_nonce'
	};
	if ( 'post_type' === select_id ) {
		data.post_type = value;
	} else {
		data.post_type = props.post_type;
		data.taxonomy = value;
	}
	$.post( 'my_ajax_url', data, function ( response ) {

		if ( undefined !== response.success && false === response.success ) {
			return;
		}

		var jsonData = $.parseJSON( response );

		/**
		 * My jsonData has three arrays in it: a list of all the posts
		 * of the selected post_type, a list of the taxonomies assigned
		 * to the selected post_type, and a list of the terms assigned to
		 * the first post_type taxonomy.
		 * 
		 * What I would like to have happen is for the options in the 
		 * selectControl elements for the taxonomy and term to update
		 * when the post_type is changed. The data is there, but how do I
		 * swap out the list of options? On the widgets admin screen, I
		 * target the select elements by ID, remove the options, and replace
		 * them.
		 */
		if ( 'post_type' === select_id ) {
			props.setAttributes( {
				taxonomy: 'post_tag', // present as a test--I can update the value of the taxonomy when the post_type changes
				options: _getOptions( jsonData.taxonomies ) // this doesn't do anything
			} );
		}
	} );
}

function _getOptions( data ) {
	var options = [];
	var i = 0;
	$.each( data, function ( key, value ) {
		options[i] = {
			value: key,
			label: value
		};
		i ++;
	} );

	return options;
}